1. Field of the Invention
The present invention relates to a method for fabricating a composite having a high specific strength and a high specific rigidity, applicable to component parts such as those of an aircraft engine and particularly to a method for fabricating a composite of metal matrix such as titan or titan alloy having reinforcing fibers such as silicon carbide fibers.
2. Description of the Related Art
Heretofore, composites formed by combining plural materials have been used widely. Metal matrix composites such as titan matrix composite (TMC) have been intensively studied and developed for component parts, such as those of aircraft engines, requiring high specific strength and high specific rigidity. The composites are reinforced in such a way that reinforcing materials typified by ceramic fibers such as silicon carbide or alumina fiber are mixed with metal matrices consisting of metals or metal alloys.
In fabricating such component parts where the metal matrix composite used, a circular disc or an annulus members such as a disc or a ring of a fan rotor is fabricated in such a manner that mono-tape preform consisting of titan alloy mixed with reinforcing fibers is composed by hot isostatic pressing (herein after referred as HIP), reinforcing fibers which have contained metal matrix by wrapping reinforcing fibers around a titan alloy drum are treated by HIP, or spiral formed reinforcing fibers which are lapped alternately between titan alloy foils are treated by HIP.
A fabricating method of composite material using mono-tape that is low in cost and capable of least dimension change when composing is as follows.
As shown in FIG. 7, a mono-tape preform 19 is made by aligning SiC reinforcing fibers 12, sandwiching the aligned fibers between metal (alloy) matrix foil 15 and hot-pressing the sandwiched materials with a hot press 17 while winding around a take-up roller 18. The mono-tape preform is convolved at a low temperature as shown in FIG. 8(a), then hot-isostatic pressed to form a ring form titan matrix composite 23 shown in FIG. 8(b).
Hot isostatic pressing is inevitable for a fabricating process of metal matrix composite as described above. In a hot isostatic pressing method, material is pressed isotropically in a metal vessel while heating. The method is utilized for adhesion of different materials, consolidation of powder material, compacting a sintered body, eliminating defects in a sintered body and others. It is necessary to improve the performance of material using such treatment of material particularly such as titan which is used under severe condition for problems arise in connection to such characteristics as fatigue or impact strength.
The hot isostatic pressing is usually carried out under the temperature and pressure condition shown in FIG. 9 with composite material in which reinforcing fibers are mixed with metal matrix. In FIG. 9, Bp denotes a pressure condition in conventional hot isostaitc pressing and Bt a temperature condition.
First, the mono-tape preform 19 is put in a HIP vessel where an initial pressure and temperature is set. In case Ti-4.5Al-3V-2Fe-2Mo alloy is used, for example, the initial pressure is set at about 30 kg/cm2 and the temperature at about 400 degrees Celsius. After that, the temperature is gradually raised to a high temperature region of HIP treatment that is a temperature of plastic deformation and diffusion and is kept there for a predetermined time. An appropriate temperature of HIP treatment of Ti-4.5Al-3V-2Fe-2Mo alloy is, for example, is about 775 degrees Celsius.
And, after the temperature is raised to a predetermined temperature, the pressure is increased to about 1200 kg/cm2. The composite is kept under the temperature and pressure for about 2 hours. Then, the temperature and pressure are lowered.
However, when a preform having a hollow inside shown in FIG. 8(a) is treated by HIP, abrupt temperature and pressure increase cause uneven deformation of the preform so that a partially excess tensile stress is arisen resulting in rupture of the reinforcing fibers.
Consequently, when a cylindrical composite is fabricated, metal foils 15, shown in FIG. 5, and spiral fibers 14 are lapped each other to make a disk formed preform 16 and the preform is hot-isostatic-pressed.
Such HIP treatment is performed by heating and pressurizing in a capsule type HIP jig 22 as shown in FIG. 6. Pressure from inner side to outer side is not generated so as not to affect the disk formed preform 16 because round shaped metal foils 15 and spiral reinforcing fibers 14 are lapped each other in the arrow direction, resulting in preventing rupture of reinforcing fibers and processing a composite material having even strength.
However, with regard to the disk formed preform 16, it still has the problem that metal foil and spiral-reinforcing fibers are expensive and the form of material processed is restricted. Lapped layers are increased when the thickness of the axial direction is large because the materials are lapped in the axial direction, which brings about high processing cost. Further, since titan is hard to carve, processing cost comes to high even if the material is easily obtained. The fabricating method has such actual drawbacks to use titan as practical parts.
As stated above, the round-formed metal matrix composite has such problems as it is unstable in strength or it is high in fabricating cost owing to the fabricating process.